Don't you find it odd that big name actors are paid the big money, are plastered all over the billboards and posters, and are generally one of the main draws for a crowd, and yet.... many indie filmmakers seem to have far less concern over who plays their roles.
Actors, they're kinda important
No matter how brilliant the script, your film will fall short if the talent isn't talented. This may seem alien to some people who are mostly used to mainstream hollywood movies where the acting usually has a minimum standard. But go watch some low budget indie films and you'll see the real difference between trained and untrained. Very few people will argue against the script being the most critical part of the production, but the actors have to convey the characters and emotions in that script.
When people watch a movie, they need to be convinced and engaged on at least one of several levels for them to stay interested. Watching believable performances is a biggie for audience engagement. There are of course exceptions, such as the cult classics of: It's so bad, it's good type marvel. But the majority have to rely on good actors.
There are many approaches, few are widely accepted
In the fair chunk of productions i've been in some way a part of, i've seen quite a few levels of casting. I was on one production where the director re-cast the main role just a day or two prior to filming, imagine how confused and conflicted that actor was. And on the opposite side i've been on a production where the director ran lines with every single auditioner, gave notes after the first reading and gave them all a second and sometimes a third read.
You could say that every director has their process, and that no particular process is precisely correct or incorrect, and you'd be somewhat accurate. But there are common traits amongst well known quality directors. Being that they are responsible for the overall production, if a casting choice is poor, it's on their shoulders. This is especially true for indie productions where many times there is no dedicated casting director, and it's up to the director and his team to lock in the talent.
So when you're gearing up for your next film, what thought have you put into who will play your supposedly enticing roles? Let's make the dangerous assumption that your script is excellent, with very deep and detailed characters. Try to imagine the big name actors in those roles and how good it would be because of their performances. Now imagine the most socially awkward people you know in those roles. Somewhere between those two imaginary thoughts lies the reality of what you're going to end up with. How much closer to the A list performances depends on how much time and effort you put into the casting process. OK, so you're on a low budget, but excuses don't make films, and we'll assume the first one is that you can't afford a casting director, so we'll work from there.
Friends and Family: NO
OK, if you're just messing around, anyone is usable, but we're talking about something you hope to get seen by the masses, get you fame and fortune, etc... I'll admit it, i've used my parents in a short film i did back in college. At some point you have to graduate to a more serious level of thinking if you truly want your film career to have a chance at going somewhere. Yes of course the exception to this is if they are properly trained actors and you put them through some sort of audition process. More on that later.
Getting serious means using serious people. After ruling out friends, family, and random people off the street, how do you go about finding real talent for your film?
Union vs non-Union
You might think that only union actors are good, and while they typically can be a safer bet, you can also find plenty of very talented actors who are not unionized. A union actor typically is very active to meet minimums/guidelines within the union, and typically has certain protection and/or benefits of being in the union, which as you can imagine attracts many serious actors.
Using union actors may not be as annoying/limiting as you might think. Even if you're a micro budget, unions these days typically have a contract for just such a production with simpler considerations than the larger production contracts. Hiring a union actor does not necessarily mean you have to pay them an upfront union dayrate, so look into the specifics in your region. In the US you'll want to visit http://www.sagindie.org/
Actors go to school too
Some actors go to college for acting, some attend workshops, some frequent courses taught by known teachers. It's not hard to find out about these things, as any actor that at least knows how to put together a resume lists all their training. Having formal training is one of those things you really should prefer over someone who just claims they know how to act. You don't have to go nuts with picking the actor with the most training, but the more they have, the more versatile they may be.
The best may not actually be the best
You may come across a very good actor, and you're going to need to step back and really consider whether or not they fit the role correctly. They may be brilliant for comedy, but not as brilliant for serious drama. Actors want good roles, and many will persist in attaining them even if they're not the right choice. Once again its up to you to make that decision. This is where another tool comes in handy: a cheap video camera. Recording auditions and getting a few opinions on who fits the role best can be a tremendous help.
Yes actors need to eat and pay rent like everyone else. One rather disturbing thing that was discussed in the forms some time back, was regarding a rather well known film course teacher who made a rather arrogant suggestion which i couldn't dig up the exact quote on, but it was to the tune of: having actors to pay to be in your movie. Respect goes all ways, and not paying actors anything won't be a good start in getting the best performance out of them. Everyone knows that low budgets are common these days, but be sure to compensate for food/travel/expenses and seriously, even 50 bucks stipend is better than zero.
When telling actors about your budget, don't be blunt about it or give attitude, or anything else negative. The best practice in my opinion is be apologetic about not being able to properly compensate them for their time. One director i've worked with on an ultra low budget even went out of his way to attend plays that his actors were in, just to give back and support them in their other projects just like they did for his project.
So no, good actors don't always cost a ton, and getting a great 'deal' on an actor can come down to how you communicate with them. If you're not excited when talking about the project, how are they to get excited?
There is no other way, you must sit down and watch auditions, in person, with sides from your film. (Sides is just a name for scene excerpts) Everyone does it, because it's that basic and necessary. Granted, if you're out to pay for a known actor to play a role, it would be pretty silly to audition them. But for everyone that's not known, you better damn audition them. The audition is where you find out if they're right for the role, as compared to other actors you audition. You should have quite a few choices for your leads, and then less and less as you go through to smaller roles. I don't think anyone auditions extras, so don't go nuts.
It's not complicated, it just takes effort
As you can see, this process isn't terribly complex, nor is it far from basic common sense. Filmmakers can fall short on casting simply because they don't put the thought into it or take it as seriously as they should. That can be said about pretty much all aspects of a production. If you can, hire a casting director who will take a lot of that burden, but many indie films just don't have the budget and it's up to the director. So long as you put real thought into your script and who you attach to it, you should do fine.